"Live and let live" was the general idea behind a recent post on r/atheism from a believer.
I mostly agree with this idea. But a comment from an atheist really appealed to why this idea is disagreeable:
"Live and let oppress I think you mean. Or live and let rape. Or live and let mutilate. Or live and let lie about aids. If you were just living, I'd be fucking fine with that."
Sure, he cites some of the more extreme examples of where "live and let live" go wrong. But here's the general issue: the believer from this post cited "live and let live" when his religion doesn't follow that same line of thought.
And obviously, Mormonism falls under this issue.
I'm not going to turn into some raging critic and share with every Mormon the history of their church, but if they ever brought the idea of "just letting people live" in some casual conversation about whatever, I'd have something to remind them of.